Scientists release new allies in battle against yellow toadflax

Star Staff
Thursday, July 11, 2019

A team of international scientists are collaborating to fight the noxious weed, yellow toadflax, Linaria vulgaris, in Montana’s Rocky Mountains with the help of a tiny insect, the shoot-galling weevil, Rhinusa pilosa.

Yellow toadflax, first introduced from Wales in the late 1600s as an ornamental and medicinal plant and to make textile dyes, is an aggressive invader. It’s listed as a noxious weed in more than 10 U.S. states, including North and South Dakota, Colorado, Nevada, New Mexico, Oregon and Idaho. The weed suppresses desirable vegetation through intense competition for limited soil moisture.

On rangelands, for example, an invasion of yellow toadflax can alter the species composition of natural communities and reduce forage production for livestock and wildlife, even under relatively undisturbed conditions. This in turn reduces rangeland value and can also lead to erosion issues.

Dr Ivo Toševski, Research Scientist in Weed Biological Control at the Centre for Agriculture and Bioscience International, has spent nearly 20 years investigating the effectiveness of several European insects – including he shoot-galling weevil – as possible biocontrol options for yellow toadflax.

Now, thanks to CABI’s research in Switzerland and following the promising release of the shoot-galling weevil in Canada in 2014, the first releases in the USA have just taken place on Montana’s Beaverhead-Deerlodge National Forest, in the Rocky Mountains.

 Dr Sharlene Sing, from the USDA Forest Service Rocky Mountain Research Station, has teamed up with Professor David Weaver, Montana State University, to release the shoot-galling weevil in Montana where yellow toadflax is threatening local ecology. “Yellow toadflax is particularly problematic because it can spread both by seeds – up to 30,000 seeds annually – and by vegetative propagation,” Sing said. “While it can be controlled by mechanical and chemical means, we are advocating a more integrated and sustainable management approach incorporating biological control, which can now be enhanced with Rhinusa pilosa.”

Dr Hariet Hinz of CABI Switzerland, said, “Our Canadian collaborator, Dr Rosemarie De Clerck-Floate from Agriculture and Agri-Food Canada found that Rhinusa pilosa established and produced galls at all release sites and also overwintered successfully in Alberta and British Columbia – even though it has not yet reached outbreak densities.”

Between 2006 and 2011 CABI tested over 100 plant species and populations to assess the host specificity of Rhinusa pilosa with the risks to native flora judged to be minimal. The weevil forms galls in the upper part of the plant shoot and significantly reduced plant height, the number of stems and biomass in a pot experiment. “Next steps for this release include monitoring the population growth of the weevil and its impact on the target weed,” said Weaver

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